Surgical exploration of the contralateral kidney in unilateral Wilms tumor has been the standard of surgical practice. During the last decade advances in noninvasive imaging techniques (ultrasound, computerized tomography and magnetic resonance imaging) have led to more accurate definition of intrarenal pathological conditions. The intuitive question presently is whether contralateral exploration remains mandatory in Wilms tumor patients. We reviewed the records of 52 consecutive children at our institutions who underwent radiological and operative staging of the Wilms tumor from 1979 to 1988. All 48 evaluable patients underwent either preoperative computerized tomography, ultrasound and/or magnetic resonance imaging. Five bilateral Wilms tumors were diagnosed preoperatively and confirmed surgically, whereas extensive operative exploration of the contralateral kidney in the other 43 cases of radiologically diagnosed unilateral disease failed to reveal any contralateral abnormality. Thus, in all patients preoperative radiological investigation was accurate to stage the disease regarding bilaterality. With modern imaging techniques and effective chemotherapy, extensive contralateral renal exploration may no longer be mandatory to manage Wilms tumor.